1. Field of the Invention
The present invention relates to a golf club shaft.
2. Description of the Related Art
A golf club shaft flexes during a swing. In particular, in the early stage of a downswing, the flexure of the shaft is caused by the inertia of a head. The shaft flexes so as that the head delays relative to the travel direction of the downswing in the early stage of the downswing. The angular acceleration of the shaft decreases gradually from the downswing to the impact to release the flexure of the shaft. This release of the flexure accelerates the speed of the head to obtain a large flight distance.
The shaft has a flexural rigidity distribution. The flexural rigidity distribution influences the flexure during the swing. The flexural rigidity distribution influences the behavior of the shaft during the swing.
A flex point (flex point ratio) has been known as an index showing the characteristics of the flexural rigidity of the shaft. A shaft having a tip side that easily forms a flexure is generally referred to as low flex point. A shaft having a rear end side that easily forms a flexure is generally referred to as high flex point. The referred low flex point or high flex point has been known in the market as the index showing the characteristics of the shaft. However, the standards of the low flex point and high flex point are not necessarily unified among the persons skilled in the art. The current situation is that a plurality of standards for the flex point exist.
Examples of the inventions relating to the flexural rigidity distribution of the shaft include Japanese Unexamined Patent Application Publication No. 2003-169871, Japanese Unexamined Patent Application Publication No. 2005-34550 and Japanese Unexamined Patent Application Publication No. 11-206932.